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Fluvial Geomorphology 143SRPP Stream Revitalization: Principles & Practices LECTURE 2 Fluvial Geomorphology Fluvial Systems: Watersheds, Hierarchical Structure, Morphological Forms, and Scale Characteristics and Classifications Winter 2019 Semester 30 September 2019 Fluvial Geomorphology Fluvial Geomorphology is the study of landforms and the processes that shape them by the transport of water and sediment through a drainage network. River Mechanics is the branch of fluvial geomorphology that quantifies the relationship between process and form in rivers and streams. Relationships are developed through a combination of field observations, physical experiments, and numerical modeling. Fluvial Geomorphology Fluvial Geomorphology is the study of landforms and the processes that shape them by the transport of water and sediment through a fluvial system. Fluvial forms: structural patterns of landforms at various spatial scales, from watersheds to channel bedforms. Fluvial processes: the action when a hydraulic force from moving water induces a landform change by transporting sediment (erosional degradation) and/or lack of force causing sediment deposition (aggradation). Hydraulic forces are dependent on flow, slope, landform\channel roughness (flow resistance) influencing local degradation and aggradation. Classic Reference: Knighton, D. 1998. Fluvial Forms and Processes: A New Perspective. Taylor and Francis Group, London. 383 p. Fluvial Systems: Dominant Controls Knighton (1998) Fluvial Systems: Dominant Controls Fluvial System landforms are dependent on dominant upstream and/or downstream controls. Fluvial Processes Vertical adjustment processes: knickpoint migration Schumm (1977, 2005) Fluvial Systems: Dominant Upstream Controls The naming of a lithology is based on the rock type: three major types: sedimentary, igneous, and metamorphic. Lithology may be either a detailed description of these characteristics or be a summary of the gross physical character of a rock. Other definitions Alluvial deposition zones occur at breaks from mountainous regions into valleys and tributary junctions. Piedmont is a landform created at the foot of a mountain or mountains by debris deposited by shifting streams. Landforms / Geological Controls New Mexico, USA (Ritter 1986) Knighton (1998) Fluvial Systems: Dominant Upstream Controls Geology: Tectonics (relief) and Lithology Source: Czech Geological Survey 1:500,000 scale Fluvial Systems: Dominant Upstream Controls Geology: Tectonics (relief) and Lithology Source: Czech Geological Survey 1:50,000 scale Praha Vitkov Fluvial Systems: Dominant Upstream Controls Geology: Tectonics (relief) and Lithology -- State of Tennessee, USA Fluvial Systems: Dominant Upstream Controls Geology: Tectonics (relief) and Lithology -- State of Tennessee, USA West TN - Quaternary Mid TN - Ordovician East TN - Precambrian Hydrologic Systems: Climate and Hydrology Dominant Upstream Controls: A Review Hydrologic System A hydrologic system is defined as a “structure” in space with a boundary, that accepts a “working medium” -- water and other inputs (air, heat energy, organic matter, chemical ions) operating internally on them to produce transformed outputs. Rainfall water Spatial and temporally distributed on the structure Stream Watershed, drainage basin, catchment outlet discharge Interactions, processes with water to produce stream flow; retention/detention soil moisture storage; evaporation, transpiration by vegetation ……. Hydrologic Systems: Climate and Hydrology Dominant Upstream Controls: A Review Distribution of precipitation input in the water budget Rainfall-Runoff Relationships Viessman & Lewis (2003) Hydrologic Systems: Hydrology and Land Use Dominant Upstream Controls – A Review Runoff Concepts: Stream Hydrographs Headwater vs downstream hydrographs baseflow Urban vs forested watershed hydrographs Wards and Trimble (2003) Fluvial Systems: Dominant Controls • Watersheds are the fundamental spatial unit in fluvial geomorphology • Drainage network patterns reflect form and process relationships. Geomorphic character is dependent on: Geology (valley shape, bank/bed material, knickpoints), watershed and riparian vegetation, channel slope, hydrology (climate), sediment supply and size, watershed position (stream order). Fluvial Processes: Force vs Resistance Erosion vs Deposition Beaver Creek, Knox County, Mill Run Section Fluvial Systems: Watersheds Watersheds: …..the fundamental unit A watershed is a topographic area that collects water, sediment and organic matter, and discharges of stream flow with transported materials through an outlet or mouth. Headwaters provide largest Headwaters surface area for a drainage Drainage network network’s supply of water, sediment, and organic matter. Mays (2005): Fig 7.1.4 Mouth Fluvial Systems: Watersheds The watershed, the functional unit of all hydrologic and geomorphic analyses. Watershed geomorphology refers to the physical characteristics of the watershed. Common measures for watersheds ≤ HUC8 Watershed Characteristics: 1. Drainage Area 2. Length (longest flow path) 3. Slope (elevation difference of flow path) 4. Shape Knighton (1998) 5. Drainage density (stream length / area ) Fluvial Systems: Watersheds Watersheds are organized as a nested hierarchy, as each small watersheds sets inside a larger one, and it sets inside a larger one and so on ……. Used by the US Geological Survey: Hydrological Unit Codes (HUC) watershed/stream identification numbers [http://nwis.waterdata.usgs.gov/tutorial/huc_def.html] 2-digit HUC first-level (region) 4-digit HUC second-level (subregion) 6-digit HUC third-level (accounting unit) 8-digit HUC fourth-level (cataloguing unit) 10-digit HUC fifth-level (watershed) 12-digit HUC sixth-level (subwatershed) Mays (2005): Fig 7.1.5 Fluvial Systems: Spatial Scales Fluvial Systems can consider landforms at different spatial scales with the largest scale starting with form the watershed/drainage network, and hierarchically reducing in scale to a segment/valley scale and/or reach channel/planform, bar unit (pool-riffle-bar elements), bedforms, and then to the channel processes bed sediment particle. ~ hierarchically nested Schumm 1977, 2005; Frothingham et al. 2002 Fluvial Systems: Spatial Scales Fluvial Spatial Scaled and Process Timescales: Timescales of various channel form components Note: Segment scale not well defined but related to spatial reflects timescale of profile gradient scale of fluvial processes and form adjustment: Knighton (1998) Drainage Network: Longitudinal Profile Examples Watershed Longitudinal Profile Elevation vs Distance headwaters 0 m downstream to mouth Concave Upward Shape ~ a function of discharge and sediment transport (increase) Bed Sediment ~ bed material size decreases in downstream direction; abrasion and selective sorting of sediment Knighton (1998) Drainage Network: Longitudinal Profile Profile concavity: influence of hardpoints and lithology Profiles more concave bed material decreases in size downstream Profiles less concave bed material remains constant in size downstream Knighton (1998) Drainage Network: Longitudinal Profile geologic knickpoints Drift Creek, Oregon Longitudinal Profile: Channel Gradient Concave upward shape quantified by logarithmic profile: Hack stream-gradient index: k = (H1 - H2)/(ln L2 - ln L1) H1 , H2 ; upstream (up/s) and downstream (d/s) elevations, respectively L1 , L2 ; up/s & d/s distances from headwaters datum 0 distance, respectively Solid line: logarithmic profile Dashed line: river profile Hack (1973) Drainage Network: Longitudinal Profile Hack Stream-gradient Index Drift Creek, Oregon canyon-section, increased slope Stream Power Stream Power is the potential energy drop is equal to the work done to the bed and banks. All of the potential energy lost as the water flows downstream must be used up in friction or work against the bed: none can be added to kinetic energy. Stream Power = Ώ = (γQS) (specific weight * gravity * discharge * slope) Unit Stream Power per channel width, where b is the width of the channel. Unit Stream Power = ω = (γQS)/b Unit Stream Power = ω = τ0V (τ0 = boundary shear stress, V = velocity) τ0 = γRhS, where Rh is the hydraulic radius = A/P (area/wetted perimeter) Cross-sectional Area (A) = bd; where d = flow depth; Q = V/A, and assumes P = b for wide and shallow Drainage Network: Longitudinal Profile - Stream Power Stream Power = energy (force x length) per unit time Stream Power is a function of discharge and slope, thus a function of watershed position; Stream Power = Ώ = (gQS) (fluid density * gravity * discharge * slope) Drift Creek, Oregon Stream Power Index = c.Ώ/w A “c” coefficient multiplied by stream power per unit channel width, with drainage area replacing Q as a surrogate for discharge. Longitudinal Profile: Geomorphic Process Continuum Process Domain Concept Geomorphic processes change from headwaters to large river corridors. Processes are also hierarchical structured from watershed scale to stream bed scale. Geomorphic analog to the River Continuum Concept. Montgomery (1999) Fluvial Systems: Classification Fluvial Geomorphic Classification is the categorization and description of the nature, origin and development of watershed and river landforms. The fundamental framework of classification is that a geomorphic unit can be classified based collectively on: [DM Haskins, 1998; USFS] 1) its origin and development (process); 2) its general structure and shape (form); 3) measurements of its dimensions and characteristics (morphology); 4) the presence and status
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